The production of mesocarbon microbeads (hereinafter referred to by the abbreviation MCMB) by separating microspheres (mesophase microspheres) formed by a process wherein a heavy oil such as a petroleum heavy oil or coal tar is subjected to a heating and carbonization treatment and having optical anisotropy from the matrix pitch is known (as disclosed in, for example, Japanese Pat. Publn. Nos. 9639/1977 and 9599/1978).
The individual microspheres or particles of the MCMB obtained in this manner may be considered to have a structure wherein polycyclic aromatic hydrocarbons which are, to a high degree, aligned and laminated in a specific direction. Because of this unique form and crystalline structure, these MCMB have high electrical, magnetic, and chemical activities, and extensive utilization thereof in various diversified fields is expected. More specifically, it has been expected to utilize these MCMB for production of various industrial materials, examples of which are: special carbon materials such as high-density isotropic carbon materials and electrical resistance carbons prepared by carbonization after molding thereof; composite materials such as electroconductive ceramics, dispersion-reinforced metals, and electroconductive plastics prepared by carbonizing the MCMB as they are and thereafter blending the resulting material with other materials; and chemical materials such as catalyst supports and packing material for chromatography. (Reference is made, for example, to Yamada and Honda: Sekiyu Gakkai-shi (Journal of the Japan Society of Petroleum Engineers) 16, 392, (1973) and "Saikin.multidot.Kuro no Sekiyu-Kagaku no Kaihatsu Jitsuyo-ka Gijutsu Shu" ("Collection (of papers on) Development and Practicalization Technology of Recent Black Petroleum Chemistry") edited by Nippon Gijutsu Keizai Sentah (Japan Technology Economy Center)(1976)).
These MCMB can be obtained by suitably heat treating heavy oil to obtain a starting-material pitch containing mesophase microspheres, mixing this pitch with an aromatic solvent such as quinoline, pyridine, or anthracene oil to selectively dissolve a matrix pitch, and recovering the mesophase microspheres (i.e., the MCMB) as the insoluble component. However, for obtaining MCMB in this manner, only laboratory techniques such as filtration and centrifugal separation have heretofore been proposed, and satisfactory techniques have not yet been established for production on an industrial scale because of several problems such as those enumerated below.
(a) Since the MCMB content in the starting-material pitch is very low (low conversion yield from the starting-material heavy oil to MCMB), a large quantity of the solvent such as quinoline or anthracene oil becomes necessary, whereby economical production is difficult. Furthermore, these solvents are toxic or have an irritating odor and thereby require large-scale measures for pollution prevention.
(b) When a suction filtration method is carried out in order to separate the MCMB after the pitch is dissolved in an aromatic solvent such as quinoline, the very small particle size of the MCMB (ordinarily from 1 to a number of tens of microns) and the formation of colloids due to solvation readily give rise to clogging of the filter material, whereby the separation requires a long time, and the operation becomes very inefficient. Furthermore, even in the case of centrifugal separation, the state of the art is such that means for treating batchwise samples of a specific quantity have merely been considered, which procedure cannot be said to be an efficient operation capable of being practiced on an industrial scale.
(c) Ordinarily, the particle size of MCMB is distributed over a range of from one micron to several tens of microns. In order to obtain a high practical value of MCMB, it is necessary to narrow the particle size distribution or to carry out a classification process for adjusting the beads to a specific particle size distribution. However, because of small sizes of the particles, an economical classification is difficult.